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Ab initio Structure Determination of [(Dimethylamino)methylene]bis[phosphonic Acid] Dihydrate from X‐Ray Powder Diffraction Data: Comparison with the Corresponding Monohydrate and Unhydrated Form
Author(s) -
Neels Antonia,
StoeckliEvans Helen,
Costisella Burhkard,
Jancke Harald,
Knudsen Kenneth D.,
Pattison Philip
Publication year - 1999
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(19990113)82:1<35::aid-hlca35>3.0.co;2-#
Subject(s) - chemistry , methylene , crystallography , x ray , ab initio , diffraction , x ray crystallography , powder diffraction , ab initio quantum chemistry methods , molecule , organic chemistry , optics , physics
The structure of [(dimethylamino)methylene]bis[phosphonic acid] dihydrate (C 3 H 11 NO 6 P 2 ⋅2 H 2 O; 1 ) was solved ab initio from synchrotron powder X‐ray diffraction data. The structure determination was based on direct methods combined with difference Fourier techniques, and the refinement was carried out using the Rietveld method. Using this high‐quality diffraction pattern, it was possible to index a second phase which corresponds to the structure of the known [(dimethylamino)methylene]bis[phosphonic acid] monohydrate ( 2 ). [(Dimethylamino)methylene]bis[phosphonic acid] dihydrate ( 1 ) is monoclinic, space group P 2 1 / c , Z =4, with a =10.6644(1), b =9.1599(1), c =10.5213(1) Å, and β =98.353(1)°. The structure analysis indicates two non‐equivalent P‐atoms in the molecule of 1 which are also observed in the corresponding monohydrate 2 and unhydrated form 3 . All three compounds exhibit extended H‐bonding networks which result in remarkably different 31 P‐NMR spectra. The [(dimethylamino)methylene]bis[phosphonic acids] 1 – 3 crystallize in the betaine‐type structure which, therefore, contains two nonequivalent P‐atoms. The −P(=O)(OH) 2 and −P(=O)(OH)O − groups of 1 – 3 are involved in a number of strong H‐bonds which can be characterized by the different 31 P‐NMR chemical shifts of the two P‐atoms of 1 – 3 .